It is known in the art that polytetrafluoroethylene (PTFE) homopolymer can be modified by including small amounts of recurring units of comonomer. For example, the art discloses a great number of comonomers that can be added to tetrafluoroethylene (TFE) and polymerized to make copolymer without losing the non-melt-processible characteristic of the basic homopolymer of tetrafluoroethylene. Some useful comonomers have been found to be chlorotrifluoroethylene (CClF.dbd.CF.sub.2 or CTFE), dichlorodifluoroethylene (CClF.dbd.CClF or CCl.sub.2 .dbd.CF.sub.2), perfluoroalkenes of 3-7 carbon atoms (R.sub.f CF.dbd.CF.sub.2 where R.sub.f is perfluoroalkyl of 1-5 carbons), and perfluoro(n-alkyl vinyl) ethers of 3-7 carbon atoms (R.sub.f --O--CF.dbd.CF.sub.2 where R.sub.f is as already defined).